This invention relates to an improved fluid seal for a piston and cylinder subassembly which transmits pressure from a pressure chamber through a cylinder structure by means of a piston to an outside object, and, more particularly, to an improved fluid seal for a disc brake caliper which transmits internal pressure to the brake pad. The term fluid as used herein includes a liquid or air medium.
Disc brakes have recently come into their own in the automotive field as a result of their superior performance when compared with the standard drum brake. Disc brakes allow a shorter stopping distance in automobiles, a more dependable braking capability and a wider range of operating conditions than the standard drum brake. However, the disadvantages of the disc brake, in that they are time consuming and costly to assemble, has lead to a rather slow acceptance in automotive circles. These disadvantages relate more to the difficulties of manufacture and the subsequent repair work rather than to the working performance of a disc brake assembly. For instance, should the O-ring seal between the cylinder and piston walls be defective or degraded through use, and dirt is allowed to enter, the precision-machined walls would become scored, occasioning a leak of brake fluid. Repair of this malfunction requires a mechanic to employ a machinist to replate and machine the surfaces scored, at a cost of much lost time and money. Furthermore, it is well known that automobile manufacturers tend to rank ease of manufacture high on their list of priorities, and this reason alone has contributed greatly to the slow adoption of the disc brake by automotive manufacturers.
A main source of difficulty of manufacture of present disc brake assemblies lies in the necessity of keeping a close tolerance between the piston and the cylinder in which the piston is inserted, thereby requiring machining to a very close tolerance and necessitating the use of several additional components to guarantee a fluid-tight seal. Thus, in addition to the close machining required in both the cylinder and the piston, an O-ring is necessary in the present form of disc brakes to insure a tight seal. This O-ring is seated in a groove which must be further machined into the cylinder walls. The end result of all this time-consuming machining and extra components is an increase in cost of the entire assembly. In operation, these close tolerances tend to wear away with time, and so require either new parts and new machining to size or a replating and subsequent machining to size of both the piston and the cylinder, all of which can be very time consuming and costly.
The present invention overcomes the aforementioned disadvantages in the difficulties of the manufacture and repair of disc brake assemblies, as well as providing new advantages in the use of a disc brake assembly.